Key words :
biodiversity,
climate change
,coral reef
,coral bleaching
,marine reserves
,mpas
,resiliance
Author
Dr. John Bruno is a marine ecologist and conservation biologist. His research is focused on understanding and conserving the structure and dynamics of marine communities. Dr...
Marine reserves and climate change: study finds no-take reserves do not increase reef resilience
3 Oct, 2008 05:26 pm
A variety of human activities have caused the recent global decline of reef-building corals. The key drivers of anthropogenic coral mortality and loss are nearly all regional- to global-scale stressors, including ocean warming, and coral predator and disease outbreaks. Yet scientists hope to mitigate these threats locally through fisheries regulations, such as the implementation of marine reserves. However, a new study tempers such optimism and suggests that marine reserves, as currently implemented, will not mitigate the impacts of climate change and other large scale disturbances.
The key drivers of anthropogenic coral mortality and loss are nearly all regional- to global-scale stressors, including ocean warming, and coral predator and disease outbreaks. Some scientists hope to mitigate these threats locally through fisheries regulations, such as the implementation of marine reserves (i.e., managed areas where fishing is not allowed, a.k.a. no-take Marine Protected Areas) designed to increase “reef resilience”. By limiting or preventing fishing and other extractive activities, marine reserves have been relatively successful in restoring populations of overharvested fish and invertebrates. Marine reserves could also, in theory, benefit corals by restoring coral reef food webs. The idea is that by maintaining healthy carnivore and herbivore populations, reef managers can prevent seaweed blooms that can kill juvenile corals. Restricting fishing would thus increase reef resiliance (which ecologists define as the return rate of an ecological system to its baseline state following a disturbance). More directly, marine reserves could benefit corals by preventing destructive fishing practices and anchor damage and if they include a terrestrial component, by reducing run-off that leads to sedimentation and nutrient pollution.
However, many reef scientists and conservationist remain skeptical about the potential of marine reserves to mitigate the effects of climate change, primarily because they cannot directly regulate or eliminate the primary culprits of anthropogenic coral loss.
In an op-ed describing the impact of the new the Papahanaumokuakea Marine National Monument in the Northwest Hawaiian Islands, Dr. Enric Sala argued, "A national monument can protect against the decimation of sharks, groupers and jacks by fishing, but it cannot protect against global threats to marine life such as global warming and marine debris...Increased temperatures and currents do not respect national monument boundaries."
William Precht, a coral reef geologist and restoration specialist for the Florida Keys National Marine Sanctuary, added, "Data from throughout the Caribbean and western Atlantic indicate that no form of local stewardship or management could have protected coral populations from their major sources of mortality (pandemic diseases, regional coral bleaching, and severe storms) or changed the overall trajectory of coral loss observed during the past few decades."
Critics of both studies could argue that many or most tropical marine reserves are not well-managed and that they might increase resiliance if enforced. This would be a fair point, but given the political and socio-economic realities of the region, poaching might be difficult or impossible to eliminate. There is growing evidence that marine reserves will not, by themselves, prevent further coral losses due to ocean warming. Restoring corals and their role as foundation species will require a range of management actions specifically directed at each of the known causes of coral population decline including directly confronting the root causes of climate change.
These views are supported by a new study published in the open access journal PloS One (Graham et al. 2008) that indicates that marine reserves have no effect on coral resiliance to ocean warming.
Approximately 45% of coral cover in the Indian Ocean was lost in 1998 due to temperature-related coral bleaching. To compare coral loss within and outside of reserves, the team re-surveyed 66 reefs in the Indian Ocean that had originally been surveyed before the 1998 mass bleaching event. The surveyed sites included reefs within nine reserves in four countries. The results indicated that "A greater proportion of [marine reserves] (71%) than fished (42%) locations showed significant declines in coral cover over the study period. There was no evidence to suggest the percent change in coral cover differed between [marine reserves] and fished areas, and in some cases declines were significantly greater in [marine reserves]."
A similar study (Jones et al. 2004) published in PNAS documented the failure of marine reserves in Papua New Guinea to mitigate the effects of the 1998 El Nino and other more local disturbances. The eight year study found that coral cover declined from 65% to 10% both inside reserves and on neighboring fished sites.
Critics of both studies could argue that many or most tropical marine reserves are not well-managed and that they might increase resiliance if enforced. This would be a fair point, but given the political and socio-economic realities of the region, poaching might be difficult or impossible to eliminate. There is growing evidence that marine reserves will not, by themselves, prevent further coral losses due to ocean warming. Restoring corals and their role as foundation species will require a range of management actions specifically directed at each of the known causes of coral population decline including directly confronting the root causes of climate change.
Literature Cited
Graham N.A.J., McClanahan T.R., MacNeil M.A., Wilson S.K., Polunin N.V.C., Jennings S., Chabanet P., Clark S., Spalding M.D., Letourneur Y., Bigot L., Galzin R., Ohman M.C., Garpe K.C., Edwards A.J. & Sheppard C.R.C. (2008) Climate Warming, Marine Protected Areas and the Ocean-Scale Integrity of Coral Reef Ecosystems. PLoS ONE, 3, e3039
Jones G.P., McCormick M.I., Srinivasan M. & Eagle J.V. (2004) Coral decline threatens fish biodiversity in marine reserves. Proc Natl Acad Sci USA, 101, 8251-8253
Key words :
biodiversity,
climate change
,coral reef
,coral bleaching
,marine reserves
,mpas
,resiliance
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